If you really want to ride, you would be wise to avoid Target, Wal-Mart and the likes. Get a quality bike assembled by a qualified mechanic at a brick and mortar bike shop. They will get you fitted on the proper bike in your price range, and most shops offer some support, be it a free tune up or minor maintenance for a year. If this is not an option, then finding a quality used bike online would be next. You want something from the big name brands, Giant, Trek, Specialized, Norco eh, etc.